Well there is nothing to my knowledge that says they changed the Bridge requirements from the 4XX series to the 5XX series so I am sure you should be okay. Again go with the rule of thumb, if it doesn't fit , don't force it :)

ST

The older bridge fit perfectly on the first 580s delivered so I'm sure you are correct. As you know I have a VERY heavy rig to get at, so it will take a bit to get the new cards installed. Thank you very much for responding and your advice. I'm going to make myself a coffee,stare at this beast for a bit and then get at it. I will of course,report back the result.